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cmd_end_transaction.go
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cmd_end_transaction.go
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// Copyright 2014 The Cockroach Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License.
package batcheval
import (
"bytes"
"context"
"fmt"
"math"
"sync/atomic"
"github.com/cockroachdb/cockroach/pkg/keys"
"github.com/cockroachdb/cockroach/pkg/roachpb"
"github.com/cockroachdb/cockroach/pkg/settings/cluster"
"github.com/cockroachdb/cockroach/pkg/storage/abortspan"
"github.com/cockroachdb/cockroach/pkg/storage/batcheval/result"
"github.com/cockroachdb/cockroach/pkg/storage/engine"
"github.com/cockroachdb/cockroach/pkg/storage/engine/enginepb"
"github.com/cockroachdb/cockroach/pkg/storage/rditer"
"github.com/cockroachdb/cockroach/pkg/storage/spanset"
"github.com/cockroachdb/cockroach/pkg/storage/stateloader"
"github.com/cockroachdb/cockroach/pkg/storage/storagebase"
"github.com/cockroachdb/cockroach/pkg/storage/storagepb"
"github.com/cockroachdb/cockroach/pkg/util/hlc"
"github.com/cockroachdb/cockroach/pkg/util/log"
"github.com/cockroachdb/cockroach/pkg/util/log/logtags"
"github.com/cockroachdb/cockroach/pkg/util/tracing"
"github.com/pkg/errors"
)
// TxnAutoGC controls whether Transaction entries are automatically gc'ed
// upon EndTransaction if they only have local intents (which can be
// resolved synchronously with EndTransaction). Certain tests become
// simpler with this being turned off.
var TxnAutoGC = true
func init() {
RegisterCommand(roachpb.EndTransaction, declareKeysEndTransaction, evalEndTransaction)
}
func declareKeysEndTransaction(
desc roachpb.RangeDescriptor, header roachpb.Header, req roachpb.Request, spans *spanset.SpanSet,
) {
declareKeysWriteTransaction(desc, header, req, spans)
et := req.(*roachpb.EndTransactionRequest)
// The spans may extend beyond this Range, but it's ok for the
// purpose of acquiring latches. The parts in our Range will
// be resolved eagerly.
for _, span := range et.IntentSpans {
spans.Add(spanset.SpanReadWrite, span)
}
if header.Txn != nil {
header.Txn.AssertInitialized(context.TODO())
abortSpanAccess := spanset.SpanReadOnly
if !et.Commit && et.Poison {
abortSpanAccess = spanset.SpanReadWrite
}
spans.Add(abortSpanAccess, roachpb.Span{
Key: keys.AbortSpanKey(header.RangeID, header.Txn.ID),
})
}
// All transactions depend on the range descriptor because they need
// to determine which intents are within the local range.
spans.Add(spanset.SpanReadOnly, roachpb.Span{Key: keys.RangeDescriptorKey(desc.StartKey)})
if et.InternalCommitTrigger != nil {
if st := et.InternalCommitTrigger.SplitTrigger; st != nil {
// Splits may read from the entire pre-split range (they read
// from the LHS in all cases, and the RHS only when the existing
// stats contain estimates), but they need to declare a write
// access to block all other concurrent writes. We block writes
// to the RHS because they will fail if applied after the split,
// and writes to the LHS because their stat deltas will
// interfere with the non-delta stats computed as a part of the
// split. (see
// https://github.com/cockroachdb/cockroach/issues/14881)
spans.Add(spanset.SpanReadWrite, roachpb.Span{
Key: st.LeftDesc.StartKey.AsRawKey(),
EndKey: st.RightDesc.EndKey.AsRawKey(),
})
spans.Add(spanset.SpanReadWrite, roachpb.Span{
Key: keys.MakeRangeKeyPrefix(st.LeftDesc.StartKey),
EndKey: keys.MakeRangeKeyPrefix(st.RightDesc.EndKey).PrefixEnd(),
})
leftRangeIDPrefix := keys.MakeRangeIDReplicatedPrefix(header.RangeID)
spans.Add(spanset.SpanReadOnly, roachpb.Span{
Key: leftRangeIDPrefix,
EndKey: leftRangeIDPrefix.PrefixEnd(),
})
rightRangeIDPrefix := keys.MakeRangeIDReplicatedPrefix(st.RightDesc.RangeID)
spans.Add(spanset.SpanReadWrite, roachpb.Span{
Key: rightRangeIDPrefix,
EndKey: rightRangeIDPrefix.PrefixEnd(),
})
rightRangeIDUnreplicatedPrefix := keys.MakeRangeIDUnreplicatedPrefix(st.RightDesc.RangeID)
spans.Add(spanset.SpanReadWrite, roachpb.Span{
Key: rightRangeIDUnreplicatedPrefix,
EndKey: rightRangeIDUnreplicatedPrefix.PrefixEnd(),
})
spans.Add(spanset.SpanReadOnly, roachpb.Span{
Key: keys.RangeLastReplicaGCTimestampKey(st.LeftDesc.RangeID),
})
spans.Add(spanset.SpanReadWrite, roachpb.Span{
Key: keys.RangeLastReplicaGCTimestampKey(st.RightDesc.RangeID),
})
spans.Add(spanset.SpanReadOnly, roachpb.Span{
Key: abortspan.MinKey(header.RangeID),
EndKey: abortspan.MaxKey(header.RangeID)})
}
if mt := et.InternalCommitTrigger.MergeTrigger; mt != nil {
// Merges write to the left side's abort span and the right side's data
// and range-local spans. They also read from the right side's range ID
// span.
leftRangeIDPrefix := keys.MakeRangeIDReplicatedPrefix(header.RangeID)
spans.Add(spanset.SpanReadWrite, roachpb.Span{
Key: leftRangeIDPrefix,
EndKey: leftRangeIDPrefix.PrefixEnd(),
})
spans.Add(spanset.SpanReadWrite, roachpb.Span{
Key: mt.RightDesc.StartKey.AsRawKey(),
EndKey: mt.RightDesc.EndKey.AsRawKey(),
})
spans.Add(spanset.SpanReadWrite, roachpb.Span{
Key: keys.MakeRangeKeyPrefix(mt.RightDesc.StartKey),
EndKey: keys.MakeRangeKeyPrefix(mt.RightDesc.EndKey),
})
spans.Add(spanset.SpanReadOnly, roachpb.Span{
Key: keys.MakeRangeIDReplicatedPrefix(mt.RightDesc.RangeID),
EndKey: keys.MakeRangeIDReplicatedPrefix(mt.RightDesc.RangeID).PrefixEnd(),
})
}
}
}
// evalEndTransaction either commits or aborts (rolls back) an extant
// transaction according to the args.Commit parameter. Rolling back
// an already rolled-back txn is ok.
func evalEndTransaction(
ctx context.Context, batch engine.ReadWriter, cArgs CommandArgs, resp roachpb.Response,
) (result.Result, error) {
args := cArgs.Args.(*roachpb.EndTransactionRequest)
h := cArgs.Header
ms := cArgs.Stats
reply := resp.(*roachpb.EndTransactionResponse)
if err := VerifyTransaction(h, args); err != nil {
return result.Result{}, err
}
// If a 1PC txn was required and we're in EndTransaction, something went wrong.
if args.Require1PC {
return result.Result{}, roachpb.NewTransactionStatusError("could not commit in one phase as requested")
}
key := keys.TransactionKey(h.Txn.Key, h.Txn.ID)
// Fetch existing transaction.
var existingTxn roachpb.Transaction
if ok, err := engine.MVCCGetProto(
ctx, batch, key, hlc.Timestamp{}, &existingTxn, engine.MVCCGetOptions{},
); err != nil {
return result.Result{}, err
} else if !ok {
// No existing transaction record was found - create one by writing it
// below in updateTxnWithExternalIntents.
txn := h.Txn.Clone()
reply.Txn = &txn
// Verify that it is safe to create the transaction record. We only need
// to perform this verification for commits. Rollbacks can always write
// an aborted txn record.
if args.Commit {
if ok, reason := cArgs.EvalCtx.CanCreateTxnRecord(reply.Txn); !ok {
return result.Result{}, roachpb.NewTransactionAbortedError(reason)
}
}
} else {
// We're using existingTxn on the reply, although it can be stale
// compared to the Transaction in the request (e.g. the Sequence,
// and various timestamps). We must be careful to update it with the
// supplied ba.Txn if we return it with an error which might be
// retried, as for example to avoid client-side serializable restart.
reply.Txn = &existingTxn
// Verify that we can either commit it or abort it (according
// to args.Commit), and also that the Timestamp and Epoch have
// not suffered regression.
switch reply.Txn.Status {
case roachpb.COMMITTED:
return result.Result{}, roachpb.NewTransactionCommittedStatusError()
case roachpb.ABORTED:
if !args.Commit {
// The transaction has already been aborted by other.
// Do not return TransactionAbortedError since the client anyway
// wanted to abort the transaction.
desc := cArgs.EvalCtx.Desc()
externalIntents, err := resolveLocalIntents(ctx, desc, batch, ms, *args, reply.Txn, cArgs.EvalCtx)
if err != nil {
return result.Result{}, err
}
if err := updateTxnWithExternalIntents(
ctx, batch, ms, *args, reply.Txn, externalIntents,
); err != nil {
return result.Result{}, err
}
// Use alwaysReturn==true because the transaction is definitely
// aborted, no matter what happens to this command.
return result.FromEndTxn(reply.Txn, true /* alwaysReturn */, args.Poison), nil
}
// If the transaction was previously aborted by a concurrent writer's
// push, any intents written are still open. It's only now that we know
// them, so we return them all for asynchronous resolution (we're
// currently not able to write on error, but see #1989).
//
// Similarly to above, use alwaysReturn==true. The caller isn't trying
// to abort, but the transaction is definitely aborted and its intents
// can go.
reply.Txn.Intents = args.IntentSpans
return result.FromEndTxn(reply.Txn, true /* alwaysReturn */, args.Poison),
roachpb.NewTransactionAbortedError(roachpb.ABORT_REASON_ABORTED_RECORD_FOUND)
case roachpb.PENDING:
if h.Txn.Epoch < reply.Txn.Epoch {
// TODO(tschottdorf): this leaves the Txn record (and more
// importantly, intents) dangling; we can't currently write on
// error. Would panic, but that makes TestEndTransactionWithErrors
// awkward.
return result.Result{}, roachpb.NewTransactionStatusError(
fmt.Sprintf("epoch regression: %d", h.Txn.Epoch),
)
} else if h.Txn.Epoch == reply.Txn.Epoch && reply.Txn.Timestamp.Less(h.Txn.OrigTimestamp) {
// The transaction record can only ever be pushed forward, so it's an
// error if somehow the transaction record has an earlier timestamp
// than the original transaction timestamp.
// TODO(tschottdorf): see above comment on epoch regression.
return result.Result{}, roachpb.NewTransactionStatusError(
fmt.Sprintf("timestamp regression: %s", h.Txn.OrigTimestamp),
)
}
default:
return result.Result{}, roachpb.NewTransactionStatusError(
fmt.Sprintf("bad txn status: %s", reply.Txn),
)
}
// Update the existing txn with the supplied txn.
reply.Txn.Update(h.Txn)
}
var pd result.Result
// Set transaction status to COMMITTED or ABORTED as per the
// args.Commit parameter.
if args.Commit {
if retry, reason := IsEndTransactionTriggeringRetryError(reply.Txn, *args); retry {
return result.Result{}, roachpb.NewTransactionRetryError(reason)
}
if IsEndTransactionExceedingDeadline(reply.Txn.Timestamp, *args) {
// If the deadline has lapsed return an error and rely on the client
// issuing a Rollback() that aborts the transaction and cleans up
// intents. Unfortunately, we're returning an error and unable to
// write on error (see #1989): we can't write ABORTED into the master
// transaction record which remains PENDING, and thus rely on the
// client to issue a Rollback() for cleanup.
//
// N.B. This deadline test is expected to be a Noop for Serializable
// transactions; unless the client misconfigured the txn, the deadline can
// only be expired if the txn has been pushed, and pushed Serializable
// transactions are detected above.
return result.Result{}, roachpb.NewTransactionStatusError(
"transaction deadline exceeded")
}
reply.Txn.Status = roachpb.COMMITTED
// Merge triggers must run before intent resolution as the merge trigger
// itself contains intents, in the RightData snapshot, that will be owned
// and thus resolved by the new range.
//
// While it might seem cleaner to simply rely on asynchronous intent
// resolution here, these intents must be resolved synchronously. We
// maintain the invariant that there are no intents on local range
// descriptors that belong to committed transactions. This allows nodes,
// during startup, to infer that any lingering intents belong to in-progress
// transactions and thus the pre-intent value can safely be used.
if mt := args.InternalCommitTrigger.GetMergeTrigger(); mt != nil {
mergeResult, err := mergeTrigger(ctx, cArgs.EvalCtx, batch.(engine.Batch),
ms, mt, reply.Txn.Timestamp)
if err != nil {
return result.Result{}, err
}
if err := pd.MergeAndDestroy(mergeResult); err != nil {
return result.Result{}, err
}
}
} else {
reply.Txn.Status = roachpb.ABORTED
}
desc := cArgs.EvalCtx.Desc()
externalIntents, err := resolveLocalIntents(ctx, desc, batch, ms, *args, reply.Txn, cArgs.EvalCtx)
if err != nil {
return result.Result{}, err
}
if err := updateTxnWithExternalIntents(ctx, batch, ms, *args, reply.Txn, externalIntents); err != nil {
return result.Result{}, err
}
// Run triggers if successfully committed.
if reply.Txn.Status == roachpb.COMMITTED {
triggerResult, err := RunCommitTrigger(ctx, cArgs.EvalCtx, batch.(engine.Batch),
ms, *args, reply.Txn)
if err != nil {
return result.Result{}, roachpb.NewReplicaCorruptionError(err)
}
if err := pd.MergeAndDestroy(triggerResult); err != nil {
return result.Result{}, err
}
}
// Note: there's no need to clear the AbortSpan state if we've successfully
// finalized a transaction, as there's no way in which an abort cache entry
// could have been written (the txn would already have been in
// state=ABORTED).
//
// Summary of transaction replay protection after EndTransaction: When a
// transactional write gets replayed over its own resolved intents, the
// write will succeed but only as an intent with a newer timestamp (with a
// WriteTooOldError). However, the replayed intent cannot be resolved by a
// subsequent replay of this EndTransaction call because the txn timestamp
// will be too old. Replays of requests which attempt to create a new txn
// record (BeginTransaction, HeartbeatTxn, or EndTransaction) never succeed
// because EndTransaction inserts in the write timestamp cache, forcing the
// call to CanCreateTxnRecord to return false, resulting in a transaction
// retry error. If the replay didn't attempt to create a txn record, any
// push will immediately succeed as a missing txn record on push where
// CanCreateTxnRecord returns false sets the transaction to aborted. In both
// cases, the txn will be GC'd on the slow path.
//
// We specify alwaysReturn==false because if the commit fails below Raft, we
// don't want the intents to be up for resolution. That should happen only
// if the commit actually happens; otherwise, we risk losing writes.
intentsResult := result.FromEndTxn(reply.Txn, false /* alwaysReturn */, args.Poison)
intentsResult.Local.UpdatedTxns = &[]*roachpb.Transaction{reply.Txn}
if err := pd.MergeAndDestroy(intentsResult); err != nil {
return result.Result{}, err
}
return pd, nil
}
// IsEndTransactionExceedingDeadline returns true if the transaction
// exceeded its deadline.
func IsEndTransactionExceedingDeadline(t hlc.Timestamp, args roachpb.EndTransactionRequest) bool {
return args.Deadline != nil && args.Deadline.Less(t)
}
// IsEndTransactionTriggeringRetryError returns true if the
// EndTransactionRequest cannot be committed and needs to return a
// TransactionRetryError.
func IsEndTransactionTriggeringRetryError(
txn *roachpb.Transaction, args roachpb.EndTransactionRequest,
) (retry bool, reason roachpb.TransactionRetryReason) {
// If we saw any WriteTooOldErrors, we must restart to avoid lost
// update anomalies.
if txn.WriteTooOld {
retry, reason = true, roachpb.RETRY_WRITE_TOO_OLD
} else {
origTimestamp := txn.OrigTimestamp
origTimestamp.Forward(txn.RefreshedTimestamp)
isTxnPushed := txn.Timestamp != origTimestamp
// Return a transaction retry error if the commit timestamp isn't equal to
// the txn timestamp.
if isTxnPushed {
retry, reason = true, roachpb.RETRY_SERIALIZABLE
}
}
// A transaction can still avoid a retry under certain conditions.
if retry && canForwardSerializableTimestamp(txn, args.NoRefreshSpans) {
retry, reason = false, 0
}
return retry, reason
}
// canForwardSerializableTimestamp returns whether a serializable txn can
// be safely committed with a forwarded timestamp. This requires that
// the transaction's timestamp has not leaked and that the transaction
// has encountered no spans which require refreshing at the forwarded
// timestamp. If either of those conditions are true, a client-side
// retry is required.
func canForwardSerializableTimestamp(txn *roachpb.Transaction, noRefreshSpans bool) bool {
return !txn.OrigTimestampWasObserved && noRefreshSpans
}
const intentResolutionBatchSize = 500
// resolveLocalIntents synchronously resolves any intents that are
// local to this range in the same batch. The remainder are collected
// and returned so that they can be handed off to asynchronous
// processing. Note that there is a maximum intent resolution
// allowance of intentResolutionBatchSize meant to avoid creating a
// batch which is too large for Raft. Any local intents which exceed
// the allowance are treated as external and are resolved
// asynchronously with the external intents.
func resolveLocalIntents(
ctx context.Context,
desc *roachpb.RangeDescriptor,
batch engine.ReadWriter,
ms *enginepb.MVCCStats,
args roachpb.EndTransactionRequest,
txn *roachpb.Transaction,
evalCtx EvalContext,
) ([]roachpb.Span, error) {
if mergeTrigger := args.InternalCommitTrigger.GetMergeTrigger(); mergeTrigger != nil {
// If this is a merge, then use the post-merge descriptor to determine
// which intents are local (note that for a split, we want to use the
// pre-split one instead because it's larger).
desc = &mergeTrigger.LeftDesc
}
iter := batch.NewIterator(engine.IterOptions{
UpperBound: desc.EndKey.AsRawKey(),
})
iterAndBuf := engine.GetBufUsingIter(iter)
defer iterAndBuf.Cleanup()
var externalIntents []roachpb.Span
var resolveAllowance int64 = intentResolutionBatchSize
if args.InternalCommitTrigger != nil {
// If this is a system transaction (such as a split or merge), don't enforce the resolve allowance.
// These transactions rely on having their intents resolved synchronously.
resolveAllowance = math.MaxInt64
}
for _, span := range args.IntentSpans {
if err := func() error {
if resolveAllowance == 0 {
externalIntents = append(externalIntents, span)
return nil
}
intent := roachpb.Intent{Span: span, Txn: txn.TxnMeta, Status: txn.Status}
if len(span.EndKey) == 0 {
// For single-key intents, do a KeyAddress-aware check of
// whether it's contained in our Range.
if !storagebase.ContainsKey(*desc, span.Key) {
externalIntents = append(externalIntents, span)
return nil
}
resolveMS := ms
resolveAllowance--
return engine.MVCCResolveWriteIntentUsingIter(ctx, batch, iterAndBuf, resolveMS, intent)
}
// For intent ranges, cut into parts inside and outside our key
// range. Resolve locally inside, delegate the rest. In particular,
// an intent range for range-local data is correctly considered local.
inSpan, outSpans := storagebase.IntersectSpan(span, *desc)
externalIntents = append(externalIntents, outSpans...)
if inSpan != nil {
intent.Span = *inSpan
num, resumeSpan, err := engine.MVCCResolveWriteIntentRangeUsingIter(ctx, batch, iterAndBuf, ms, intent, resolveAllowance)
if err != nil {
return err
}
if evalCtx.EvalKnobs().NumKeysEvaluatedForRangeIntentResolution != nil {
atomic.AddInt64(evalCtx.EvalKnobs().NumKeysEvaluatedForRangeIntentResolution, num)
}
resolveAllowance -= num
if resumeSpan != nil {
if resolveAllowance != 0 {
log.Fatalf(ctx, "expected resolve allowance to be exactly 0 resolving %s; got %d", intent.Span, resolveAllowance)
}
externalIntents = append(externalIntents, *resumeSpan)
}
return nil
}
return nil
}(); err != nil {
log.Fatalf(ctx, "error resolving intent at %s on end transaction [%s]: %s", span, txn.Status, err)
}
}
// If the poison arg is set, make sure to set the abort span entry.
if args.Poison && txn.Status == roachpb.ABORTED {
if err := SetAbortSpan(ctx, evalCtx, batch, ms, txn.TxnMeta, true /* poison */); err != nil {
return nil, err
}
}
return externalIntents, nil
}
// updateTxnWithExternalIntents persists the transaction record with
// updated status (& possibly timestamp). If we've already resolved
// all intents locally, we actually delete the record right away - no
// use in keeping it around.
func updateTxnWithExternalIntents(
ctx context.Context,
batch engine.ReadWriter,
ms *enginepb.MVCCStats,
args roachpb.EndTransactionRequest,
txn *roachpb.Transaction,
externalIntents []roachpb.Span,
) error {
key := keys.TransactionKey(txn.Key, txn.ID)
if TxnAutoGC && len(externalIntents) == 0 {
if log.V(2) {
log.Infof(ctx, "auto-gc'ed %s (%d intents)", txn.Short(), len(args.IntentSpans))
}
return engine.MVCCDelete(ctx, batch, ms, key, hlc.Timestamp{}, nil /* txn */)
}
txn.Intents = externalIntents
txnRecord := txn.AsRecord()
return engine.MVCCPutProto(ctx, batch, ms, key, hlc.Timestamp{}, nil /* txn */, &txnRecord)
}
// RunCommitTrigger runs the commit trigger from an end transaction request.
func RunCommitTrigger(
ctx context.Context,
rec EvalContext,
batch engine.Batch,
ms *enginepb.MVCCStats,
args roachpb.EndTransactionRequest,
txn *roachpb.Transaction,
) (result.Result, error) {
ct := args.InternalCommitTrigger
if ct == nil {
return result.Result{}, nil
}
if ct.GetSplitTrigger() != nil {
newMS, trigger, err := splitTrigger(
ctx, rec, batch, *ms, ct.SplitTrigger, txn.Timestamp,
)
*ms = newMS
return trigger, err
}
if crt := ct.GetChangeReplicasTrigger(); crt != nil {
return changeReplicasTrigger(ctx, rec, batch, crt), nil
}
if ct.GetModifiedSpanTrigger() != nil {
var pd result.Result
if ct.ModifiedSpanTrigger.SystemConfigSpan {
// Check if we need to gossip the system config.
// NOTE: System config gossiping can only execute correctly if
// the transaction record is located on the range that contains
// the system span. If a transaction is created which modifies
// both system *and* non-system data, it should be ensured that
// the transaction record itself is on the system span. This can
// be done by making sure a system key is the first key touched
// in the transaction.
if rec.ContainsKey(keys.SystemConfigSpan.Key) {
if err := pd.MergeAndDestroy(
result.Result{
Local: result.LocalResult{
MaybeGossipSystemConfig: true,
},
},
); err != nil {
return result.Result{}, err
}
} else {
log.Errorf(ctx, "System configuration span was modified, but the "+
"modification trigger is executing on a non-system range. "+
"Configuration changes will not be gossiped.")
}
}
if nlSpan := ct.ModifiedSpanTrigger.NodeLivenessSpan; nlSpan != nil {
if err := pd.MergeAndDestroy(
result.Result{
Local: result.LocalResult{
MaybeGossipNodeLiveness: nlSpan,
},
},
); err != nil {
return result.Result{}, err
}
}
return pd, nil
}
if ct.GetMergeTrigger() != nil {
// Merge triggers were handled earlier, before intent resolution.
return result.Result{}, nil
}
log.Fatalf(ctx, "unknown commit trigger: %+v", ct)
return result.Result{}, nil
}
// splitTrigger is called on a successful commit of a transaction
// containing an AdminSplit operation. It copies the AbortSpan for
// the new range and recomputes stats for both the existing, left hand
// side (LHS) range and the right hand side (RHS) range. For
// performance it only computes the stats for the original range (the
// left hand side) and infers the RHS stats by subtracting from the
// original stats. We compute the LHS stats because the split key
// computation ensures that we do not create large LHS
// ranges. However, this optimization is only possible if the stats
// are fully accurate. If they contain estimates, stats for both the
// LHS and RHS are computed.
//
// Splits are complicated. A split is initiated when a replica receives an
// AdminSplit request. Note that this request (and other "admin" requests)
// differs from normal requests in that it doesn't go through Raft but instead
// allows the lease holder Replica to act as the orchestrator for the
// distributed transaction that performs the split. As such, this request is
// only executed on the lease holder replica and the request is redirected to
// the lease holder if the recipient is a follower.
//
// Splits do not require the lease for correctness (which is good, because we
// only check that the lease is held at the beginning of the operation, and
// have no way to ensure that it is continually held until the end). Followers
// could perform splits too, and the only downside would be that if two splits
// were attempted concurrently (or a split and a ChangeReplicas), one would
// fail. The lease is used to designate one replica for this role and avoid
// wasting time on splits that may fail.
//
// The processing of splits is divided into two phases. The first phase occurs
// in Replica.AdminSplit. In that phase, the split-point is computed, and a
// transaction is started which updates both the LHS and RHS range descriptors
// and the meta range addressing information. (If we're splitting a meta2 range
// we'll be updating the meta1 addressing, otherwise we'll be updating the
// meta2 addressing). That transaction includes a special SplitTrigger flag on
// the EndTransaction request. Like all transactions, the requests within the
// transaction are replicated via Raft, including the EndTransaction request.
//
// The second phase of split processing occurs when each replica for the range
// encounters the SplitTrigger. Processing of the SplitTrigger happens below,
// in Replica.splitTrigger. The processing of the SplitTrigger occurs in two
// stages. The first stage operates within the context of an engine.Batch and
// updates all of the on-disk state for the old and new ranges atomically. The
// second stage is invoked when the batch commits and updates the in-memory
// state, creating the new replica in memory and populating its timestamp cache
// and registering it with the store.
//
// There is lots of subtlety here. The easy scenario is that all of the
// replicas process the SplitTrigger before processing any Raft message for RHS
// (right hand side) of the newly split range. Something like:
//
// Node A Node B Node C
// ----------------------------------------------------
// range 1 | | |
// | | |
// SplitTrigger | |
// | SplitTrigger |
// | | SplitTrigger
// | | |
// ----------------------------------------------------
// split finished on A, B and C | |
// | | |
// range 2 | | |
// | ---- MsgVote --> | |
// | ---------------------- MsgVote ---> |
//
// But that ideal ordering is not guaranteed. The split is "finished" when two
// of the replicas have appended the end-txn request containing the
// SplitTrigger to their Raft log. The following scenario is possible:
//
// Node A Node B Node C
// ----------------------------------------------------
// range 1 | | |
// | | |
// SplitTrigger | |
// | SplitTrigger |
// | | |
// ----------------------------------------------------
// split finished on A and B | |
// | | |
// range 2 | | |
// | ---- MsgVote --> | |
// | --------------------- MsgVote ---> ???
// | | |
// | | SplitTrigger
//
// In this scenario, C will create range 2 upon reception of the MsgVote from
// A, though locally that span of keys is still part of range 1. This is
// possible because at the Raft level ranges are identified by integer IDs and
// it isn't until C receives a snapshot of range 2 from the leader that it
// discovers the span of keys it covers. In order to prevent C from fully
// initializing range 2 in this instance, we prohibit applying a snapshot to a
// range if the snapshot overlaps another range. See Store.canApplySnapshotLocked.
//
// But while a snapshot may not have been applied at C, an uninitialized
// Replica was created. An uninitialized Replica is one which belongs to a Raft
// group but for which the range descriptor has not been received. This Replica
// will have participated in the Raft elections. When we're creating the new
// Replica below we take control of this uninitialized Replica and stop it from
// responding to Raft messages by marking it "destroyed". Note that we use the
// Replica.mu.destroyed field for this, but we don't do everything that
// Replica.Destroy does (so we should probably rename that field in light of
// its new uses). In particular we don't touch any data on disk or leave a
// tombstone. This is especially important because leaving a tombstone would
// prevent the legitimate recreation of this replica.
//
// There is subtle synchronization here that is currently controlled by the
// Store.processRaft goroutine. In particular, the serial execution of
// Replica.handleRaftReady by Store.processRaft ensures that an uninitialized
// RHS won't be concurrently executing in Replica.handleRaftReady because we're
// currently running on that goroutine (i.e. Replica.splitTrigger is called on
// the processRaft goroutine).
//
// TODO(peter): The above synchronization needs to be fixed. Using a single
// goroutine for executing Replica.handleRaftReady is undesirable from a
// performance perspective. Likely we will have to add a mutex to Replica to
// protect handleRaftReady and to grab that mutex below when marking the
// uninitialized Replica as "destroyed". Hopefully we'll also be able to remove
// Store.processRaftMu.
//
// Note that in this more complex scenario, A (which performed the SplitTrigger
// first) will create the associated Raft group for range 2 and start
// campaigning immediately. It is possible for B to receive MsgVote requests
// before it has applied the SplitTrigger as well. Both B and C will vote for A
// (and preserve the records of that vote in their HardState). It is critically
// important for Raft correctness that we do not lose the records of these
// votes. After electing A the Raft leader for range 2, A will then attempt to
// send a snapshot to B and C and we'll fall into the situation above where a
// snapshot is received for a range before it has finished splitting from its
// sibling and is thus rejected. An interesting subtlety here: A will send a
// snapshot to B and C because when range 2 is initialized we were careful set
// synthesize its HardState to set its Raft log index to 10. If we had instead
// used log index 0, Raft would have believed the group to be empty, but the
// RHS has something. Using a non-zero initial log index causes Raft to believe
// that there is a discarded prefix to the log and will thus send a snapshot to
// followers.
//
// A final point of clarification: when we split a range we're splitting the
// data the range contains. But we're not forking or splitting the associated
// Raft group. Instead, we're creating a new Raft group to control the RHS of
// the split. That Raft group is starting from an empty Raft log (positioned at
// log entry 10) and a snapshot of the RHS of the split range.
//
// After the split trigger returns, the on-disk state of the right-hand side
// will be suitable for instantiating the right hand side Replica, and
// a suitable trigger is returned, along with the updated stats which represent
// the LHS delta caused by the split (i.e. all writes in the current batch
// which went to the left-hand side, minus the kv pairs which moved to the
// RHS).
//
// These stats are suitable for returning up the callstack like those for
// regular commands; the corresponding delta for the RHS is part of the
// returned trigger and is handled by the Store.
func splitTrigger(
ctx context.Context,
rec EvalContext,
batch engine.Batch,
bothDeltaMS enginepb.MVCCStats,
split *roachpb.SplitTrigger,
ts hlc.Timestamp,
) (enginepb.MVCCStats, result.Result, error) {
// TODO(tschottdorf): should have an incoming context from the corresponding
// EndTransaction, but the plumbing has not been done yet.
// TODO(andrei): should this span be a child of the ctx's (if any)?
sp := rec.Tracer().(*tracing.Tracer).StartRootSpan(
"split", logtags.FromContext(ctx), tracing.NonRecordableSpan,
)
defer sp.Finish()
desc := rec.Desc()
if !bytes.Equal(desc.StartKey, split.LeftDesc.StartKey) ||
!bytes.Equal(desc.EndKey, split.RightDesc.EndKey) {
return enginepb.MVCCStats{}, result.Result{}, errors.Errorf("range does not match splits: (%s-%s) + (%s-%s) != %s",
split.LeftDesc.StartKey, split.LeftDesc.EndKey,
split.RightDesc.StartKey, split.RightDesc.EndKey, rec)
}
// Preserve stats for pre-split range, excluding the current batch.
origBothMS := rec.GetMVCCStats()
// TODO(d4l3k): we should check which side of the split is smaller
// and compute stats for it instead of having a constraint that the
// left hand side is smaller.
// Compute (absolute) stats for LHS range. Don't write to the LHS below;
// this needs to happen before this step.
leftMS, err := rditer.ComputeStatsForRange(&split.LeftDesc, batch, ts.WallTime)
if err != nil {
return enginepb.MVCCStats{}, result.Result{}, errors.Wrap(err, "unable to compute stats for LHS range after split")
}
log.Event(ctx, "computed stats for left hand side range")
// Copy the last replica GC timestamp. This value is unreplicated,
// which is why the MVCC stats are set to nil on calls to
// MVCCPutProto.
replicaGCTS, err := rec.GetLastReplicaGCTimestamp(ctx)
if err != nil {
return enginepb.MVCCStats{}, result.Result{}, errors.Wrap(err, "unable to fetch last replica GC timestamp")
}
if err := engine.MVCCPutProto(ctx, batch, nil, keys.RangeLastReplicaGCTimestampKey(split.RightDesc.RangeID), hlc.Timestamp{}, nil, &replicaGCTS); err != nil {
return enginepb.MVCCStats{}, result.Result{}, errors.Wrap(err, "unable to copy last replica GC timestamp")
}
// Initialize the RHS range's AbortSpan by copying the LHS's.
if err := rec.AbortSpan().CopyTo(
ctx, batch, batch, &bothDeltaMS, ts, split.RightDesc.RangeID,
); err != nil {
return enginepb.MVCCStats{}, result.Result{}, err
}
// Compute (absolute) stats for RHS range.
var rightMS enginepb.MVCCStats
if origBothMS.ContainsEstimates || bothDeltaMS.ContainsEstimates {
// Because either the original stats or the delta stats contain
// estimate values, we cannot perform arithmetic to determine the
// new range's stats. Instead, we must recompute by iterating
// over the keys and counting.
rightMS, err = rditer.ComputeStatsForRange(&split.RightDesc, batch, ts.WallTime)
if err != nil {
return enginepb.MVCCStats{}, result.Result{}, errors.Wrap(err, "unable to compute stats for RHS range after split")
}
} else {
// Because neither the original stats nor the delta stats contain
// estimate values, we can safely perform arithmetic to determine the
// new range's stats. The calculation looks like:
// rhs_ms = orig_both_ms - orig_left_ms + right_delta_ms
// = orig_both_ms - left_ms + left_delta_ms + right_delta_ms
// = orig_both_ms - left_ms + delta_ms
// where the following extra helper variables are used:
// - orig_left_ms: the left-hand side key range, before the split
// - (left|right)_delta_ms: the contributions to bothDeltaMS in this batch,
// itemized by the side of the split.
//
// Note that the result of that computation never has ContainsEstimates
// set due to none of the inputs having it.
// Start with the full stats before the split.
rightMS = origBothMS
// Remove stats from the left side of the split, at the same time adding
// the batch contributions for the right-hand side.
rightMS.Subtract(leftMS)
rightMS.Add(bothDeltaMS)
}
// Note: we don't copy the queue last processed times. This means
// we'll process the RHS range in consistency and time series
// maintenance queues again possibly sooner than if we copied. The
// intent is to limit post-raft logic.
// Now that we've computed the stats for the RHS so far, we persist them.
// This looks a bit more complicated than it really is: updating the stats
// also changes the stats, and we write not only the stats but a complete
// initial state. Additionally, since bothDeltaMS is tracking writes to
// both sides, we need to update it as well.
{
preRightMS := rightMS // for bothDeltaMS
// Various pieces of code rely on a replica's lease never being unitialized,
// but it's more than that - it ensures that we properly initialize the
// timestamp cache, which is only populated on the lease holder, from that
// of the original Range. We found out about a regression here the hard way
// in #7899. Prior to this block, the following could happen:
// - a client reads key 'd', leaving an entry in the timestamp cache on the
// lease holder of [a,e) at the time, node one.
// - the range [a,e) splits at key 'c'. [c,e) starts out without a lease.
// - the replicas of [a,e) on nodes one and two both process the split
// trigger and thus copy their timestamp caches to the new right-hand side
// Replica. However, only node one's timestamp cache contains information
// about the read of key 'd' in the first place.
// - node two becomes the lease holder for [c,e). Its timestamp cache does
// not know about the read at 'd' which happened at the beginning.
// - node two can illegally propose a write to 'd' at a lower timestamp.
//
// TODO(tschottdorf): why would this use r.store.Engine() and not the
// batch?
leftLease, err := MakeStateLoader(rec).LoadLease(ctx, rec.Engine())
if err != nil {
return enginepb.MVCCStats{}, result.Result{}, errors.Wrap(err, "unable to load lease")
}
if (leftLease == roachpb.Lease{}) {
log.Fatalf(ctx, "LHS of split has no lease")
}
replica, found := split.RightDesc.GetReplicaDescriptor(leftLease.Replica.StoreID)
if !found {
return enginepb.MVCCStats{}, result.Result{}, errors.Errorf(
"pre-split lease holder %+v not found in post-split descriptor %+v",
leftLease.Replica, split.RightDesc,
)
}
rightLease := leftLease
rightLease.Replica = replica
gcThreshold, err := MakeStateLoader(rec).LoadGCThreshold(ctx, rec.Engine())
if err != nil {
return enginepb.MVCCStats{}, result.Result{}, errors.Wrap(err, "unable to load GCThreshold")
}
if (*gcThreshold == hlc.Timestamp{}) {
log.VEventf(ctx, 1, "LHS's GCThreshold of split is not set")
}
txnSpanGCThreshold, err := MakeStateLoader(rec).LoadTxnSpanGCThreshold(ctx, rec.Engine())
if err != nil {
return enginepb.MVCCStats{}, result.Result{}, errors.Wrap(err, "unable to load TxnSpanGCThreshold")
}
if (*txnSpanGCThreshold == hlc.Timestamp{}) {
log.VEventf(ctx, 1, "LHS's TxnSpanGCThreshold of split is not set")
}
// Writing the initial state is subtle since this also seeds the Raft
// group. It becomes more subtle due to proposer-evaluated Raft.
//
// We are writing to the right hand side's Raft group state in this
// batch so we need to synchronize with anything else that could be
// touching that replica's Raft state. Specifically, we want to prohibit
// an uninitialized Replica from receiving a message for the right hand
// side range and performing raft processing. This is achieved by
// serializing execution of uninitialized Replicas in Store.processRaft
// and ensuring that no uninitialized Replica is being processed while
// an initialized one (like the one currently being split) is being
// processed.
//
// Since the right hand side of the split's Raft group may already
// exist, we must be prepared to absorb an existing HardState. The Raft
// group may already exist because other nodes could already have
// processed the split and started talking to our node, prompting the
// creation of a Raft group that can vote and bump its term, but not
// much else: it can't receive snapshots because those intersect the
// pre-split range; it can't apply log commands because it needs a
// snapshot first.
//
// However, we can't absorb the right-hand side's HardState here because
// we only *evaluate* the proposal here, but by the time it is
// *applied*, the HardState could have changed. We do this downstream of
// Raft, in splitPostApply, where we write the last index and the
// HardState via a call to synthesizeRaftState. Here, we only call
// writeInitialReplicaState which essentially writes a ReplicaState
// only.
rightMS, err = stateloader.WriteInitialReplicaState(
ctx, rec.ClusterSettings(), batch, rightMS, split.RightDesc,
rightLease, *gcThreshold, *txnSpanGCThreshold,
)
if err != nil {
return enginepb.MVCCStats{}, result.Result{}, errors.Wrap(err, "unable to write initial Replica state")
}
if !rec.ClusterSettings().Version.IsActive(cluster.VersionSplitHardStateBelowRaft) {
// Write an initial state upstream of Raft even though it might
// clobber downstream simply because that's what 1.0 does and if we
// don't write it here, then a 1.0 version applying it as a follower
// won't write a HardState at all and is guaranteed to crash.
rsl := stateloader.Make(rec.ClusterSettings(), split.RightDesc.RangeID)
if err := rsl.SynthesizeRaftState(ctx, batch); err != nil {
return enginepb.MVCCStats{}, result.Result{}, errors.Wrap(err, "unable to synthesize initial Raft state")
}
}
bothDeltaMS.Subtract(preRightMS)
bothDeltaMS.Add(rightMS)
}
// Compute how much data the left-hand side has shed by splitting.
// We've already recomputed that in absolute terms, so all we need to do is
// to turn it into a delta so the upstream machinery can digest it.
leftDeltaMS := leftMS // start with new left-hand side absolute stats
recStats := rec.GetMVCCStats()
leftDeltaMS.Subtract(recStats) // subtract pre-split absolute stats
leftDeltaMS.ContainsEstimates = false // if there were any, recomputation removed them
// Perform a similar computation for the right hand side. The difference
// is that there isn't yet a Replica which could apply these stats, so
// they will go into the trigger to make the Store (which keeps running
// counters) aware.
rightDeltaMS := bothDeltaMS
rightDeltaMS.Subtract(leftDeltaMS)
var pd result.Result
// This makes sure that no reads are happening in parallel; see #3148.
pd.Replicated.BlockReads = true
pd.Replicated.Split = &storagepb.Split{
SplitTrigger: *split,
RHSDelta: rightDeltaMS,
}
return leftDeltaMS, pd, nil
}
// mergeTrigger is called on a successful commit of an AdminMerge transaction.
// It writes data from the right-hand range into the left-hand range and
// recomputes stats for the left-hand range.
func mergeTrigger(
ctx context.Context,
rec EvalContext,
batch engine.Batch,
ms *enginepb.MVCCStats,
merge *roachpb.MergeTrigger,